Re: Efficiency of CREATE TABLE AS

Brian Herlihy <btherl(at)yahoo(dot)com(dot)au> writes:
> If I do the following
> CREATE TABLE foo AS SELECT * FROM bar
> and a sequential scan is chosen as the plan (in particular, no
> ordering required), will the rows be written directly into the new
> table?

Yes ... actually, the plan has nothing to do with it.

> I am concerned about the case where there may be many
> gigabytes of data being copied between these two tables. And my
> precise concern is that the data may be stored temporarily before
> being placed in the new table, slowing things down.

No. The computed tuples go to the new table, noplace else. See
intorel_receive() and related code.

regards, tom lane